63 F85 Cutlass

I have a BW T10 im goinfg to be putting in swapping from auto to manual. Havn't removefd the cover or tail yet but here's the issue. 1-2 and 3-4 shifter forks seem to be moving fine, but i believe the trannys been in reverse since i got it, and i cant get it to disengage. Any suggestions? ive never messed with the insides of a tranny before

-Ryan